Update test dummy application defaults to remove warnings

[zzak]

Affected gems:

• actionmailbox
• activestorage
• actiontext

This fixes the following warning:

DEPRECATION WARNING: Using legacy connection handling is deprecated. Please set
`legacy_connection_handling` to `false` in your application.

The new connection handling does not support `connection_handlers`
getter and setter.

Read more about how to migrate at: https://guides.rubyonrails.org/active_record_multiple_databases.html#migrate-to-the-new-connection-handling
 (called from require at ~/.gem/ruby/3.1.0/gems/zeitwerk-2.4.2/lib/zeitwerk/kernel.rb:34)

[eugeneius]

👍

Active Storage and Action Text also have dummy apps, which have the same problem:

https://buildkite.com/rails/rails/builds/77642#459f0e23-956a-4900-b577-692fc85b0c69/1067-1083
https://buildkite.com/rails/rails/builds/77642#cc40736e-2f80-45e3-af04-7d1db31f59ce/1067-1091

[zzak]

@eugeneius Thanks! I will patch those too and put them in this same commit

[zzak]

@eugeneius Done! 🙏

[zzak]

Ok I see some actually relevant errors in CI:

ActiveStorage::PreviewTest#test_previewing_on_the_writer_DB:
--
  | NotImplementedError: `while_preventing_writes` is only available on the connection_handler with legacy_connection_handling
  | /rails/activerecord/lib/active_record/connection_adapters/abstract/connection_handler.rb:104:in `while_preventing_writes'
  | /rails/activestorage/test/models/preview_test.rb:58:in `block in <class:PreviewTest>'

Will work on fixing these first.

[zzak]

@eugeneius I fixed the ActionMailbox tests and pulled in some commits from #42543 that fixed the ActiveStorage tests. This should be good to go 🙏

[pixeltrix]

@zzak thanks! 👍🏻

[vipera]

Would it be possible to backport this change to 6.1, as I've actually run into a bug using ActiveStorage::VariantWithRecord without the service delegate when calling processed on an ActiveStorage variant using the track_variants feature:

undefined method `service' for #<ActiveStorage::VariantWithRecord:...>